Filter device with a segmented design

ABSTRACT

A filter device comprising: filter elements with wall openings on their internal ring and filter elements with wall openings on their external ring the elements being alternately stacked; an external housing; an internal filter conduit, which is configured through the internal ring walls of the filter elements and is connected to filter elements in addition to a first fluid conduit via the internal ring wall openings; and an essentially annular filter material that is located between two respective filter elements. The front faces of the filter elements have essentially planar, peripheral external and internal sealing surfaces, which, when the filter elements rest one on top of the other, clamping filter material therebetween, lie above one another and are rough.

BACKGROUND OF THE INVENTION

The invention pertains to a filter device with elements which arearranged in a row on top of one another and are mainly cylindrical inshape and which can be mainly flow-charged radially, alternatively fromoutside and inside; the device also has a ring-shaped filter materialbetween two of these elements. Generic filter devices are described inthe document EP 0152903 B1, reference to which publication is made intotality, in order to avoid repetitions.

Thereby a ring-shaped sheet-type filtering material is charged throughwith the fluid to be filtered coming out of the end-side openings ofhollow-cylindrical flow-charging elements which are arranged on top ofone another on a fluid line meant for fluid to be filtered and areconnected to it, and passed on into hollow-cylindrical dischargeelements through end-side openings and then forwarded out of these intoa filtrate chamber. The elements should preferably be made of materialhaving a long life span, like metal, especially steel or plastic andinclude between themselves respectively a filter material sheet that canbe replaced after getting worn out.

Filter devices of this type have very high requirements/specifications.Apart from safely and completely fulfilling the required filteringperformances, one should be able to ensure a reliable, trouble-freeoperation, as a failure of the filter device would not only lead tounusable products, but will also mean enormous losses due to standstill.Generic filter devices can be used in various carriers, e.g. forfiltering out solid substances or even liquids from gases, e.g. forseparating oil from compressed air (oil separator), for removingmicro-organisms from beverages, from nutritive broth of fermentingagents and more similar items. Thereby these filter devices have towithstand temperatures up to 200, sometimes up to 300° C. and pressuresin the range of 16 bar to 20 or even 30 bar. They should not fail if thedesigned capacity is exceeded by two times or even three times,sometimes even at short notice.

Particularly in production of groceries and beverages, like say inbreweries, apart from the already addressed requirements, very often italso has to be ensured that the filtrates are sterile after passingthrough the filter. If this sterilisation effect fails, which cannotalways be identified immediately, then large production quantities canbe rendered unusable.

A problem with filtering plants according to the state-of-the-arttechnology lies in the sealing of the filter material gaskets againstthe charging and discharging elements. Till now, the filter materialgaskets are held between the charging and discharging elements by a moreor less plane sealing edge running all around inside and outside,whereby the elements get pressed on one another, in order to ensure asealing through the thrust pressure. In a preferred design form, thisstack of elements is pressed, one on top of the other, by a tie rodrunning through the centre axis of the filter, and the filter medium issealed at the edge regions.

It has been seen in the case of known generic filter plants, that duringassembly a twisting of the ring-type charging elements against eachother is possible, and this could result in damage and in some caseseven shearing off of the filter membranes. The holding of the filtermembrane discs in the sealing region had in the past led to a channelformation in case of higher load and hence to leakage. This occurredparticularly when in case of increased pressure the fluid could form apath in the soft membrane material. The tightness of the membranevis-à-vis the elements therefore still left scope for improvement.

It is an object of the invention to provide a filter device wherein thesealing of the filter elements is improved.

SUMMARY OF THE INVENTION

The object is achieved by the invention by means of a filter device withlargely hollow cylinder-shaped filter elements stacked alternately aboveone another and having inner ring wall openings, and filter elementshaving outer ring wall openings; an outer housing which with the outerring walls of the filter elements forms an outer housing fluid chamber,which ends in a second fluid pipeline; a filter inner pipeline which isformed by the inner ring walls of the filter elements and is connectedto the filter elements as well as to a first fluid pipeline through theinner ring wall openings; between every two of these filter elements amostly ring-shaped filter material is arranged, whereby the filterelements are largely hollow cylinder shaped and have an inner ring wall,an outer ring wall as well as an upper and lower end face with openings,whereby the filter elements have openings either on their radial outerwall or inner wall, whereby a fluid line can be created from the innerpipeline of the filter through the inner wall openings in the inner wallof the hollow cylinder-shaped filter elements and through the end-sideopenings of the same through the ring-shaped filter material and throughthe end-side openings into the next hollow cylinder shaped filterelement having outer openings and through whose openings arranged in theouter walls, into the filtrate chamber or a housing chamber or, in caseof reverse flow, a fluid line can be created from outside to the innerpipeline; a cover part for tight closing of the upper filter element;and a base part for locking the lowest filter element; whereby the endfaces of the filter elements largely have flat peripheral outer andinner sealing surfaces which, because of the filter elements lying ontop of one another, get to lie above one another on account of filtermaterial get jammed in between, and become uneven.

As already explained, for a filter device of the type mentioned here, itis of great significance that it is completely sealed, i.e. it should beruled out that the filtering fluid gets through the filter devicewithout filtration, i.e. bypasses the filter material. For this it isvery important that the filter material, especially in the case of afilter device as described further above is tightly held between theelements, i.e. between the respective outer and inner ring walls. Thiscan basically be supported, in that the elements are surrounded at theirouter and inner edge with a sealing skirting.

Due to the fact that now uneven or rough sealing surfaces are foreseen,any twisting of the elements against the filter material is avoided andhence any damage of the membranes due to the rotation movement isprevented. Furthermore, in this way a channel formation can beprevented, as in the sealing region different densities of the filtermaterial exercise a slightly lower thrust pressure. Unevenness in thiscase means roughness that does not harm the intermediately lyingmembrane, but exercises an impression to the extent that a twisting ofthe membrane is avoided. Even the channel formation is prevented as theroughness tightens the membranes due to the impression.

It is therefore the principle of this invention that the filtermaterial—with or without strainers—should be fastened torsion-free inthe sealing ring, as in case of a rotation of the filter elements, e.g.on cooling of the tie rod, the membranes sometimes get damaged or evensheared off. The filter material—with or without support-strainers—isimpressed according to the principle through the roughness of thesealing surfaces and then lies untwistable on the corresponding surfaceor the corresponding surrounding region. The element is also heldsimilarly in untwistable on the membrane. Furthermore, one can obtain adesired elasticity a reliable sealing locking between the elements andthe filter materials in between, as explained further details below.

Process-technically it is favourable, in case the unevenness of theouter and inner sealing surfaces are more or less same. As method forcreating the unevenness of the sealing surfaces, one has the possibilityof sand blasting, ball blasting, laser processing, milling or any otherprocessing method known to the expert, for the material of the sealingedges. What is important is that the unevenness is not so high that itpenetrates the filter material or seriously damages it; it must becreated in such a way that only an impression of the sealing region ofthe membrane will take place, but no puncturing or cutting of the same.To a certain degree, the choice of roughness depends also on the filtermaterial used; filter materials that disintegrate easily withstandlesser roughness than highly elastic, expandable materials with goodtensile strength like PTFE or aramide.

Process-technically it is also meaningful to have the unevennesses ofthe outer and inner sealing surfaces by and large with the sameroughness. For supporting the filter material and keeping away coarseimpurities, it is advisable to connect at least one strainer before orafter the filter material in flow direction. Production-technically itcould be sensible to design the cylinder-shaped filter element inseveral parts, at least consisting of an inner ring and an outer ring aswell as, if required, one or several strainers. It could also beadvantageous if one strainer can be placed on the end face. It ispreferable that the filter material is arranged at a distance to thestrainer. In the flow direction at least one strainer can be connectedeither before or after the filter material—in this way, coarseimpurities can be pre-filtered.

It can be favourable if the filter elements, the housing and the coverpart and base part, are at least partly made of plastic. This gives theadvantage of simple and cost-effective production. But for filters withparticularly long life span or those subjected to high mechanical load,it can be advantageous if the filter elements, the housing and the coverpart and base part are at least partly made of metal, like steel.

In a preferred design form, the cylinder-shaped elements are designed inseveral parts, having at least one inner ring and an outer ring (as wellas, if required, one or several strainers). Thereby at least onestrainer can be fitted into the outer ring wall and/or the inner ringwall. The filter material can be arranged at a distance from thestrainer—however, it could also partly lie on it.

The ring-shaped filter material can be solely made of or in combinationof ceramic, metal, natural or synthetic polymers, synthetic resin-ionexchanger, polymers of halogenated hydrocarbons, teflon, porcelain,glass, metal, paper, cellulose, felt, leather, asbestos, glass, sawdust,pumice stone, titanium dioxide, and, if required, also be made of two orseveral layers. On account of the filter material it could be necessaryto design the filter membrane in such a way that it consists ofdifferent substances. Thus, for example, one may desire a sandwich-typestructure or even an arrangement in which the filter membrane has aholding/supporting region which has a different composition than thefiltering region. The ring-shaped filter material can in some cases ofapplication, e.g. in case of ion exchange resins, be regeneratable. Thefilter material in its entire edge region works together with theelements to provide a sealing effect. Because of the principle ofsealing the filter material in its entire edge region with or againstthe hollow cylinder-shaped elements, with the help of the uneven sealingsurfaces, it is possible in the case of a generic filter device to avoidthe above mentioned disadvantages. For pressure-sensitive filtermaterials, like glass sinters or other brittle materials it could beadvantageous if the flat filter material has a holding/supporting regionhaving a different composition than the filter region.

To ensure the thrust pressure on the element compound, which isimportant for the sealing tightness of the filter, it is preferable ifin the inner pipeline a tie rod is foreseen, on which the hollowcylinder-shaped filter elements and the ring-shaped filter material areinserted and which is fixed in the upper cover cap and the lower covercap and thus tightens the filter elements/filter material stack. Thiscould be in the form of a long bolt and, if required, can be supportedwith a compression spring under tension. Providing a tie rod is howevernot important—one can resort to any other measure which ensures apressure on one another of the filter elements stack while completelysealing the combination through pressing on one another of the sealingsurfaces, as is well known to the expert.

If the filter elements do not reveal sufficient stability against thepressure which has to be applied on the elements, then it could befavourable if the cylinder-shaped elements have support walls runningradially to the axis of the inner line and vertically to the end facesof the element.

The openings in at least one end face of the hollow cylinder-shapedelements, through which the filter material is then charged or thefiltrated enters into the filter element, can be a hole type or slottedtyped (see FIG. 8) and/or in the type of a strainer.

While mounting the filter—i.e. while placing the individual chargingelements on top of one another and tightening the charging elementscombination, the roughened surfaces of the sealing region of adjacentcharging elements come to lie on the opposite sides of a filter materialgasket which get locally compressed and tightened on account of theunevenness, so that any twisting of the filter material against thecharging elements and any twisting of the charging elements against oneanother can be avoided.

Each filter element that works as charging lead element has at least oneinflow opening and at least one discharge opening, which is designed inthe inner wall or in the outer wall, as well as filter materialaccesses, out of which the “filter ”-medium flows into the filter deviceas per the invention, whereby the purified filtrate is then drawn offinto the filtrate chamber of the filter device through the dischargeopenings.

In case of reverse charging direction—which can be done for “cleaning”the filter—the fluid to be filtered flows from outside to inside.

Here one must refer to the initially described flow direction with innerwall and designate the closing region of each filter element inwards,i.e. in case of the known double pipe structure, the regioncorresponding to the inner pipes. Similarly the region under the outerwall having a larger diameter than the pipes, has to be designated. Theinflow opening of the outer wall or the discharge opening in the innerwall results in the fact that in each case a defined “chamber” iscreated, into which the filtrate once flows in from inside, is divertedand then passes through a filter gasket which is situated above or belowit. Such a chamber, which could also have discharge openings or inflowopenings distributed over the circumference, has roughened sealingsurfaces or sealing strips above and below running around on the insideor outside, against which the elements can be pressed to produce asealing effect.

In particular cases, e.g. if there are very highly stable membranes likeceramic membranes or highly stable plastic membranes (nylon, fluorated,hydrocarbons, aramides etc.) the filter material itself may besufficient; a strainer or supporting element will not be necessary.

The element of a filter device as per the invention can basically bedesigned in one piece. Production-wise it is however advisable tomanufacture the element in the form of an inner ring wall and outer ringwall which are connected to one another by strainers. The strainer canbe welded or pasted on its inner and outer edge with the inner and outeredge. Particularly if a strainer is arranged before and after the filtermaterial, it is advisable to connect the strainer to the inner ring walland the outer ring wall in a detachable manner, perhaps by a screwingmechanism. One can also think of clamping or using clamp screws.

It is extremely important for sealing tightness of the filter device andthe sealing combination of the elements with the filter material, thatfor all elements and on all inner ring walls and outer ring walls of theelements the necessary pressure between the adjacent elements alwaysprevails, in order to ensure the sealing pressing of the filtermaterial. Particularly if relatively thin filter material is used, whichis also relatively less expandable, then the pressure between outer orinner ring walls of the elements can drop significantly due tooccurrence of settlement.

For holding the elements together, generally the upper and lower holdersof the elements are tightened against one another with a tie rod. Thetie rod could be a long bolt guided through the centre of the filterdevice coinciding with the axis of the filter device.

A filter device as per the invention, as described above, can bebasically operated with the filter material. As the flow-throughcapacity is also a function of the available filtering surface, it isadvantageous to accommodate as many filter units as possible in aparticular space. An economic utilisation of space can be achieved byrelative elements. In order to fulfil this, the invention furtheradvises that in filter devices of the type being discussed here,especially in a filter device with one or several features describedabove, to use plastic membranes as filter material. The startingmaterial for such membranes is marketed, for example, also under thebrand name GORE-TEX: Such a filter material consists of a membrane thatis filter-active.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantageous extensions of the invention can be obtained from thesub-claims, as well as the subsequent description of the encloseddrawing showing only design examples. The following are shown:

FIG. 1 A partly sectioned view of a design example of a filter device asper the invention;

FIG. 2 principle diagram of the fluid course in a filter device as perthe invention;

FIG. 3 a perspective view of the filter device shown in FIG. 1 withremoved housing;

FIG. 4 two elements of the filter device as per the invention with afilter membrane lying in between, shown enlarged;

FIG. 5 an alternate design of an element as per the invention;

FIG. 6 an alternate element that is opened inwards and closed towardsthe outer pipe;

FIG. 7 a top view on an element as shown in FIG. 4 and FIG. 5 withsupport walls;

FIG. 8 a further alternative element with slit-type openings in the endfaces, in top view;

FIG. 9 filter material in top view; and

FIG. 10 Schematic diagram of the charge flow of the filter material in afilter device between two filter elements.

DETAILED DESCRIPTION

A filter device 10 for fluids has been shown and described, i.e. forfiltering of gases, liquids or similar items in process-technicalplants, as described in details above at the beginning. This filterdevice is particularly suited for gas filtration. An example of filtersas per the invention, as shown in FIG. 1, are oil separators, waterseparators, ion exchangers and similar items.

FIG. 1 shows a perspective depiction of a preferred extension of adevice as per the invention, whereby a window is cut in a housing 20.One can clearly identify the elements alternately lying above oneanother with strainer-type end faces 7 and alternately outer and inneropenings which allow entry of fluid from the inner pipe 18 or thehousing chamber 16 which is formed between the outer ring walls 9 andthe housing 20.

FIG. 2 gives the diagram of the fluid flow in the filter device 10,whereby here the inflow of the fluid to be filtered takes place throughthe inner pipeline 18 and the outflow of the filtered fluid takes placethrough the housing chamber 16. One can clearly identify that the fluidto be filtered reaches the filter device 10 through the inlet pipe 12,passes through the elements 1 a through the inner wall openings 4, andis then filtered through the filter membrane 2 which is fixed tightly onthe end wall 7 with openings, enters it through the end wall 7 of thenext element 1 b and then leaves it through the outer wall openings 3 inthe housing chamber or the outer chamber 16 and is then guided out in afiltered condition through the second fluid pipe 14 which is connectedhere as discharge pipe. The filter device 10 shown in FIG. 2 is verymuch enlarged in order to show the filter material 2 clearly and is alsodepicted very thickly—this in no way corresponds to a technicalrealisation of the invention but is only meant for the purpose of betterunderstanding. As one can see, the elements 1 b are closed on theinside, i.e. towards the inflow pipe 12, and the elements 1 a have anopening 4 towards the inflow pipe 12.

In the example shown in FIG. 2, the fluid to be filtered flows throughthe openings of the elements 1 a open towards the inflow pipe 12, andthen after diversion of the flow almost by 90° flows through the filtermaterial 2 and then again after a flow diversion by about 90° throughfurther elements 1 b which are opened outwards, that is towards thefiltrate chamber 16. The elements 1 a, 1 b are supported by upper andlower skirting or cover caps 28 or 30.

The fluid to be filtered flows from the first fluid pipe 12 into therespective filter elements 1 a, or more precisely the inlet pipe 12leads into a filter inner pipe 18 which can also be formed by therespective inner ring walls 8 of all filter elements 1 a, 1 b, that areeither opened or not opened towards it.

As shown more precisely in FIG. 3, which presents a perspective view ofthe inner filter region without housing 20, the filter device 10 ismainly made up of elements 1 a, 1 b, 11 a, 11 b, 22 a, 22 b, that is,mainly made up of circular ring-shaped elements which have an outer ringwall 9 and an inner ring wall 8 and end faces 7, i.e. respectively anelement base and an element top with openings. In the design exampleshown in FIG. 2, the outer ring wall 9 and the inner ring wall 8 areheld together by strainer element bases or tops 7, which are thenrespectively connected in a shape-hugging manner to the outer ring wall9, as one can see in the drawing.

As further shown in FIG. 3 and also in FIG. 4, the inner ring wallopenings 4 are designed as inflow openings and the outer ring wallopenings 3 operated as outflow openings are designed in the outer ringwall 8 or the inner ring wall 9, as holes.

In FIG. 4 one can see that on the outer ring wall 9 and the inner ringwall 8 there are uneven support surfaces 53 or 54 running all around, onwhich the filter material 2 rests with its edge region right through.Thus the filter material 2 is held completely tight-sealed between twofilter elements 1 a, 1 b which again have corresponding sand-blastedsealing surfaces 53 and 54 on their lower side.

In FIG. 4 one can see two outflow openings 3 or inflow openings 4;however, each filter element can have either more or lesser outflowopenings or inflow openings.

FIGS. 3 and 9 show a design form of a filter membrane 2, which oftenfinds application as filter material 2 as per the invention. This filtermembrane here is a PTFE-membrane and consists of one layer. As one cansee in the perspective diagram shown in FIG. 3, the filter material 2 orthe filter membrane reveal recesses in the edge region, whose advantageshave already been described above. In the FIGS. 5 to 7 alternativedesign forms of the elements are shown. As one can see from the abovedescription, for a filter device 10 as per the invention it is necessaryto have different elements 1 a, 1 b or 11 a, 11 b or 22 a, 22 b workingtogether.

The filter element 11 a shown in FIG. 5 is provided with openings 3 intothe housing chamber 16, which could have any shape that would beconducive with the stability of the filter element. Here they aredesigned as holes. These openings 3 allow a free exit of the filtratethat flows out of the filter material 2 into the filter element 11 bopen outwards, through the openings in the end face 7 of the filterelement 1 a. The filter elements receive the fluid to be filtered, whichis not yet purified and guide it through the openings in their end faces7 into the filter material 2. As the filter elements 11 a are constantlysubjected to impurities in this flow direction, it may be necessary toclean the elements 11 a separately, or even to replace them or to makethem of a material that is insensitive to impurities. The filterelements 11 b which are opened outward and which in this flow directioncome in contact with the filtered fluid, would not required cleaning sofrequently and could be made of any cost-effective material which is notso resistant. Thereby, in order to absorb pressure exercised on thefilter elements it would be advisable to provide radial/star-shapedsupport walls 32 in the individual elements 11 a, 11 b, 1 a, 1 b, 22 a,22 b, which will prevent any distortion of the filter elements in thedirection of the filter main axis, which again might lead to leakages inthe arrangement. The number of radial support walls 32 is not verycritical; due to reasons of increased mechanical load, provision ofsupport walls 32 can be particularly advantageous in case of heavilyweakened supporting ring walls 8, 9, as shown in FIG. 6.

FIG. 5 shows a further preferred design form of the openings in the ringwall surface of the filter elements 22 b as radial slots, which would bedesirable due to reasons of material and resistance. Of course, evencircular openings or any other suitable form of openings can be foreseenin the end faces 7 of the filter elements 1 a, 1 b, 11 a, 11 b, 22 a, 22b, whereby the size and shape of the openings have restrictions onlywith respect to stability of the filter elements.

As shown in FIG. 8, it is also possible to design the openings in theend faces 7 as slots.

A sealing of the filter material 2 against the inner pipeline and outerpipeline is necessary. This is done, in that the filter material sheet 2is strongly compressed and held by the pressure of the filter elementsin the edge region and sealing region by the roughened sealing surfaces53, 54 in such a way, that any flow-through of fluid is not possible.

FIG. 10 shows in details the use of the filter membrane 2 as per theinvention under a charging filter element 1 b with support walls. Tosimplify the diagram, the upper end face of the charging filter elementhas been left out. The fluid to be filtered enters here—shown clearly bythe arrows—through open side walls of the filter element gasket 1 b outof the housing chamber 16, then through the strainer-type perforationinto the lower end face 7 of the element 1 b, the element base, into thefilter material sheet 2 lying below it, leaves the filter material in afiltered condition and runs into a end face 7 provided with openings,into a structurally similar filter element 1 a, which is open towardsthe filter inner pipeline 18 and closed towards the housing chamber 16,then to the filter inner pipeline 18 and from there into the filterfluid pipeline 12. The lower filter element is here shown in the diagramas end element and therefore does not have any openings on its base.Such filter arrangements can be stacked on top of one another at anyheights, whereby for achieving a satisfactory filtration, the sealing ofthe filter materials against the filter element sealing surfaces is veryimportant, in order that no impure fluid can bypass the membranes 2.

The features of the invention indicated in the above description, thedrawing and the claims can be important individually as well as in anyrandom combination for realizing the invention in its variousextensions.

1-16. (canceled)
 17. A filter device comprising first filter elementsand second filter elements which are substantially hollow cylindrical inshape having inner ring walls defining an inner pipeline and outer ringwalls, the first and second filter elements being alternately stackedone above another, the first filter elements having openings in theinner ring walls communicating with the inner pipeline and the secondfilter elements having openings in the outer ring walls; an outerhousing spaced from the outer ring walls an defining therewith an outerfluid chamber, wherein the openings in the outer walls of the secondfilter elements communicate with the outer fluid chamber; an inlet fluidpipeline communicating with the inner pipeline and an outlet fluidpipeline communicating with the outer fluid chamber; a substantiallyhollow ring shaped filter material positioned between the alternatingfirst and second filter elements, wherein the first and second filterelements each have upper and lower end faces with openings, wherein thefilter material is held between the faces such that there is a flowdirection from the inlet pipeline to the inner pipeline, through theinner ring wall openings and the ring shaped filter material, throughthe outer ring wall opening to the outer fluid chamber and the outletfluid pipeline; upper and lower cover parts for sealing the filterelements together with the filter material; and the end faces of thefilter elements each have an inner ring sealing surface and an outerring sealing surface for sealing the ring shaped filter materialtherebetween.
 18. A filter device according to claim 17, wherein atleast one of the inner and outer ring sealing surfaces of a filterelement comprises first and second offset surfaces which mate withcorresponding first and second offset surfaces in an adjacent filterelement.
 19. A filter device according to claim 18, wherein the firstand second offset surfaces are located on the inner ring sealingsurface.
 20. A filter device according to claim 18, wherein the outerring sealing surfaces and inner ring sealing surface have the sameroughness.
 21. A filter device according to claim 17, wherein the filterelements, the housing, the cover part and base part are made at leastpartly made of plastic.
 22. A filter device according to claim 17,wherein the filter elements, the housing, the cover part and base partare made at least partly of metal.
 23. A filter device according toclaim 17, wherein at least one strainer is located at at least one ofbefore and after the filter material in the flow direction.
 24. A filterdevice according to claim 17, wherein at least one strainer is locatedon the end faces of the filter elements.
 25. A filter device accordingto claim 24, wherein the filter material is located a distance from thestrainer.
 26. A filter device according to claim 17, wherein a tie rodis provided in the inner pipeline on which the hollow cylindrical filterelements and the ring-shaped filter material are inserted, wherein thetie rod is fixed in the upper cover part and the lower cover part.
 27. Afilter device according to claim 17, wherein the filter elements havesupport walls running radial to an axis of the inner pipeline andvertically to the end faces of the filter elements.
 28. A filter deviceaccording to claim 17, wherein the filter material has a holding regionwhich has a different composition than a filtering region.
 29. A filterdevice according to claim 28, wherein the filter material has an edgeregion which is roughened.
 30. A filter device according to claim 28,wherein the filter material comprises a material selected from the groupconsisting of ceramic, metal, natural or synthetic polymers, syntheticresin-ion exchangers, polymers of halogenated hydrocarbons, teflon,porcelain, glass, metal, paper, cellulose, felt, leather, asbestos,glass, sawdust, pumice stone, titanium dioxide and mixtures thereof.